Thursday, January 24, 2008

7.12 I see 'little' people

(Gulliver's Travels: Lilliput hallucination?)

Occasionally, an elderly patient with counting finger vision reports seeing black cats darting across the room, zig-zag lines, little people moving about (hence the term "Lilliput hallucination"), various pulsating geometric shapes, closing and opening curtains, etc. Needless to say, the patient is very anxious ("Am I losing my mind?") and family members are equally concerned - until it is explained that these are a form of visual hallucination.

A Swiss gentleman by the name of Charles Bonnet documented in 1760 that his grandfather, nearly blinded from cataracts, complained of seeing vivid phantom images - hence the name, Charles Bonnet Syndrome (CBS). If you have never heard of it, you are not alone.

First and foremost, patients with CBS are mentally healthy. The hallucination is not the pharmacologically-induced type or from psychosis/dementia, but are, in a way, similar to the phantom-limb syndrome. In the latter, amputees can still sense itch and pain in the now removed limbs.

What causes CBS? Theories abound, e.g., sensory deprivation, dream activation, creative visual cortex, etc. The only way to make sure is to map the brain with MEG or fMRI during hallucination, at least to see which brain area is activated. This will be extremely difficult, if not impossible.

Not everyone experiences CBS, though - in only about 15% of low-vision patients according to one study. There are other studies, statistical numbers may vary but all are in the low percentiles. Some clinicians have reported CBS in patients with recent vision loss. We have encountered only patients with long-term (i.e., years of) loss. So, the onset of CBS may be patient-specific. The cause of vision loss per se, however, does not appear important.

Unlike the real pain in phantom-limb syndrome, CBS cannot be or even needs to be treated. Just know that patients with CBS do not have any psychiatric issues. Instead, their vision needs to be re-evaluated and possibly further rehabilitated.